#include <iostream>

using namespace std;

const int N = 5e4 + 10;
int a[N];
int len, n, k, m;

int calc(int x)
{
	int ret = 0;
	for(int i = 0; i <= n; i++)
	{
		int j = i + 1;
 		while(j <= n && a[j] - a[i] < x) j++;
 		ret += j - i - 1;
 		i = j - 1;
	}
	return ret;
}

int main()
{
	cin >> len >> n >> k;
	for(int i = 1; i <= n; i++) cin >> a[i];
	a[++n] = len;
	
	int l = 1, r = len; 
	while(l < r)
	{
		int mid = (l + r + 1) >> 1;
		int t = calc(mid);
		if(t <= k) l = mid;
		else r = mid - 1; 
	}
	
	cout << l << endl;
	
	return 0;
}
